1. Field of the Disclosure
The present disclosure relates to a drive motor control apparatus for a vehicle, a motor control system, a method for correcting a rotation angle of a motor, a program for performing the correcting method, and a rotation detecting apparatus.
2. Description of Related Art
For example, a drive motor control apparatus for controlling a motor of a vehicle having the motor as a drive power source, such as an electric vehicle, a hybrid vehicle, an electric train, is described in JP-A-H10-215504 and U.S. Pat. No. 5,896,283 which are incorporated by reference. The above drive motor control apparatus is configured to detect a rotation angle of the motor and to control energization of the motor based on the detection result. More specifically, the above drive motor control apparatus controls a drive device, such as an inverter, for energizing the motor.
JP-A-H10-215504 and U.S. Pat. No. 5,896,283 describe a control device provided with a resolver that serves as a rotation angle sensor for detecting the rotation angle of the motor. The resolver is a known rotation angle detecting sensor having a stator and a rotor that rotates synchronously with the rotation of an output shaft of the motor. The resolver outputs a rotation detection signal in accordance with a change of reluctance between the rotor and the stator based on the position of the rotor. In other words, the resolver outputs the rotation detection signal in accordance with the rotation angle of the motor. Note that in the description below, the stator and the rotor of the resolver are referred to as a “resolver stator” and a “resolver rotor” in order to distinguish from the stator and the rotor of the motor.
A specific configuration of the resolver will be described with an example of a two-phase resolver, which has phases different from each other by an electrical rotation angle of 90 degrees, and which outputs two rotation detection signals. The two-phase resolver has a primary coil provided to one of the resolver rotor and the resolver stator, and has a secondary coil provided to the other one. An energization signal of a constant frequency is supplied to the primary coil, and the secondary coil outputs two rotation detection signals, which are made by modulating the amplitude of the energization signal, and which have phases different from each other by 90 degrees.
The resolver outputs the rotation detection signal of an analog signal. Thus, when the rotation angle of the motor is detected 14 using the resolver, a resolver digital converter (RDC) is used in combination with the resolver, in general. Typically, the RDC converts the rotation detection signal from the resolver into angle data that is digital data indicating the rotation angle of motor. Then, the drive motor control apparatus controls energization of the motor based on the angle data from the RDC.
Note that, in a realistic condition, the two rotation detection signals outputted from the resolver have equivalent amplitudes and, are not offset from each other. Also, furthermore, the two rotation detection signals have the phase difference of a control value (90 degrees in the above example). The RDC functions idealistically when the rotation detection signals received from the resolver satisfy the above idealistic condition, and thereby the RDC provides a proper degree of detection accuracy of the rotation angle.
Also, in addition to the resolver, the rotation angle sensor for sensing the rotation angle of the motor includes, for example, an incremental encoder, which outputs a signal (or a pulse) for the rotation of the motor by a certain angle, and which outputs another signal (or another pulse) for the one rotation of the motor. Also, the rotation angle sensor may be an absolute encoder that outputs angle data indicating a rotation angle when the motor rotates a certain angle rotation. For example, the rotation angle sensor may be a sensor that includes a vertical Hall element and a magnetic resistance element (MRE) as described in JP-A-2008-185406 and US-A-2009-0295375, which are incorporated by reference. The above sensor outputs a signal in accordance with the rotation angle. As above, there are various kinds of the rotation angle sensors.
For example, in practice, the resolver may output the rotation detection signals that are different from the above idealistic signals due to various causes, such as “manufacturing variation” of the resolver. As a result, the two-phase resolver signals may have different amplitudes, the offset, or the phase error. In other words, the rotation detection signals from the resolver may include an error caused by the manufacturing variation. The “manufacturing variation” includes variation in the shape of the resolver rotor, the feature of each coil of the resolver, or the gap between the resolver rotor and the resolver stator.
If the rotation detection signals from the resolver include errors as above, angle data outputted from the RDC may accordingly include errors, and thereby a degree of detection accuracy of the rotation angle may deteriorate disadvantageously. Specifically, in the above deterioration state, even when the motor rotates at a constant speed, the angle data from the RDC becomes non-proportional to time, and thereby having a non-linear feature.
Because the drive motor control apparatus controls the energization of the motor based on the rotation angle of the motor known from the angle data of the RDC, the energization of the motor may be inappropriate for the actual rotation angle of the motor, and thereby causing degraded control accuracy of the motor.
For example, even when a vehicle drives at a constant speed, and also the driver does not change the accelerator pedal operation (or does not change the force for pressing the pedal), the vehicle may be accelerated or decelerated in a fore-and-aft direction unwantedly. The above unwanted phenomenon happens in the following process. Because angle data from the RDC includes the error, the angle data indicates a rotation angle different from the actual rotation angle of the motor. Thus, generated torque of the motor may be changed erroneously when the above erroneous data is used for the control of the motor. Thus, even when the driver does not change the accelerator pedal operation, the vehicle may be accelerated or decelerated erroneously. Thus, occupants of the vehicle including the driver may feel uneasy, as a result.
Also, the rotation angle sensor other than the resolver may have the erroneous detection signal issues caused by the manufacturing variation similar to the resolver, and thereby the other rotation angle sensor may have disadvantages similar to the resolver.